The invention relates to an apparatus for cutting up hard and brittle material, such as semiconductor material in general and more particularly to such a method using a gang saw having sawblades arranged side by side in a vibration proof frame, the blades being studded with diamond granules.
Gang saws of this general nature are suited for cutting up hard, brittle materials and minerals like rock or quartz, and particularly, semiconductor material. The cutting up of semiconductor crystals, particularly those that are known as AIII-BV compounds such as, for instance, the well known two phase semiconductor material consisting of a compound of indium antimonide with inclusions of nickel antimonide, or also gallium arsenide, gallium phosphide or indium phosphide presents various difficulties when using known methods and apparatus. Typical examples of apparatus used for this purpose are high speed diamond saws as well as wire and gang saws. With the methods known heretofore, one obtains, for instance, relatively large cutting losses where semiconductor rods are to be divided into wafers, and the surface roughness of these wafers is relatively high. If semiconductor rods with a large diameter are cut up, cut surfaces are obtained which are not completely parallel to each other, and the surface is therefore not flat. In addition, the cutting takes a relatively long time and the depth of the saw cut is limited. The preparation of perfectly parallel and plane cut surfaces is particularly important if materials of high value are to be fabricated with a diameter of, say, 50 mm or more with low cutting losses as well as high surface quality and dimensional faithfulness.
A known gang saw for cutting quartz crystals into thin slices which are used in the manufacture of quartz oscillators contains a crank drive which acts via a sliding head on a mounting frame coupled to the former. In this mounting frame, a separate clamping frame for receiving the sawblades is provided. The blades are inserted with lateral play and are held in their position by special alignment means. The tightening forces, amounting to up to several tons, are taken up exclusively by the clamping frame. These large clamping forces can easily lead to a deformation of the clamping frame and it is therefore difficult to align the blades accurately in the mounting frame and to maintain the parallel direction of motion of the individual blades (U.S. Pat. No. 3,326,071).
The sawblades are therefore clamped in detachable mounting profiles which are bolted on and protrude between the legs of these mounting profiles. The mounting profiles which surround the one yoke beam of the clamping frame rest with their legs against the yoke beam over the entire length without play, while the mounting profiles surrounding the other yoke beam of the clamping frame are braced against the yoke beam in places and are cantilevered at their ends. The other yoke beam of the clamping frame is connected with the legs of the latter movably in the clamping direction, and is supported in the tightened position by adjustable supporting means, e.g., lock nuts. Through these design features, the bending of the clamping frame, which occurs under the tensioning action of the sawblades, is supposedly compensated. The cutting forces are obtained by feeding abrasives to the sawblades. These abrasives, contained in a liquid mixture, however, attack not only the material to be cut up, but also the sawblades and the wear is therefore accordingly heavy (German Auslegeschrift No. 2,039,699).
In an arrangement disclosed in U.S. Pat. No. 2,774,194 the cutting blades of a device for cutting up semiconductor material are provided with an ultrasonic drive and vibrate in the cutting direction. The blades are held over the entire length of their upper edge by means of a clamping device. With this known arrangement, however, the individual sawblades can be arranged only at a relatively large spacing from each other and the manufacture of thin wafers is therefore not possible.
For cutting up silicon rods, diamond cutting disks which are equipped with sintered-in diamond studding have also been used. These diamond disks are arranged side by side on a shaft and are separated from each other by spacers. Such tools for cutting semiconductor material, however, are suited only for relatively small saw depths. Therefore, only wafers with a relatively small area can be produced therewith. Steel bands, the surfaces of which are provided with diamond grains, can also be used for cutting rock and hard metals, as is well known. The diamond grains can be mechanically pressed into the band or may also be bonded by electroplating with a surface finish of a nickel or chromium coating. These bands are provided with cuts which are likewise filled with diamond grains. However, these bands are relatively thick and therefore result in correspondingly large cutting losses.